This invention relates to the detection of defects in the cording of cord reinforced tire fabric and in particular, the detection of missing or overlapping cords. The invention is particularly useful for detecting defects in steel cord reinforced fabric, but also can be used to detect defects in fabric having other types of reinforcing cords, so long as the radiation absorbtion coefficient of the cord is not the same as for rubber. For convenience, the following specification describes the invention in connection with steel reinforced fabric.
Tire fabric for vehicle tires is usually made in a continuous calendering process wherein rubber latex is calendered onto a plurality of reinforcing strands so as to form a sandwich having a strand core with a layer of rubber on each side. In the course of the calendering operation, it is possible for one or more of the strands to be missing or for two strands to overlap, either of which constitutes a defect. It is also possible for the spacing of the strands to become non-uniform so that the number of strands in a section of fabric is below a required minimum. Since the rubber is opaque, defects must be detected by non-optical means.
There are a number of non-optical ways of detecting the presence of reinforcing strands, and defect detection methods involving scanning the fabric and simply counting the total number of strands have been suggested. This method is not satisfactory since it is important that each small section of the fabric be defect-free, and within a relatively small area of fabric a one strand difference in the predicted count could be caused by the plus/minus one count digitizing error inherent in digital counting systems rather than by a missing cord.
Accordingly, the present invention provides a sensitive cord counting system in which digitization errors do not make the cord count ambiguous.